1. Field of the Invention
Embodiments of the invention refer to the field of medical technology and relates to a shielding apparatus and shielding structures for magnetic resonance imaging and to a method for operating a magnetic resonance imaging scanner.
2. Description of the Related Art
In nuclear magnetic resonance or magnetic resonance imaging (MRI=Magnetic Resonance Imaging), powerful static magnetic fields force atom nuclei to perform a precision movement about the field direction and the nuclei are excited by resonance by radio frequency alternating electromagnetic fields. After the alternating fields are switched off, the nuclei return in the starting directions thereof, wherein the decay times (relaxation times) are characteristic of different tissue types, thereby enabling precise imaging.
Today, MRI examinations are part of the daily routine in radiological diagnostics, posing no risk for the patients under normal examination conditions, apart from an occasional decreased sense of well-being. However, an increasing number of patients has implants which are made entirely or partially of a metallic material and can cause problems during the examination, and in the worst case can even injure the patients. The material that is used and the geometry of the implant, as well as the position thereof in relation to the radio frequency alternating fields that are employed, play a role. Some implants, for example, function very well as antennas for the alternating fields and heat up considerably due to the induction currents that are generated. Consequently, thermal damage to the surrounding tissue may ensue. On the other hand, the radio frequency alternating fields may trigger a malfunction in electronic implants or an undesirable restart with preset starting parameters (“power-on reset”).
For this reason, the diagnostic benefit of an examination by magnetic resonance imaging must be carefully weighed against the risk of disadvantageous side effects. An additional hindering aspect is that, for example, the heating of implanted electrodes depends on the respective scan parameters of the examination, and in particular on the positioning thereof in the alternating electromagnetic field, so that in clinical practice it is frequently impossible to make reliable predictions as to the effects to be expected. All these factors consequently lead to patients that have implants to be generally excluded from an examination by magnetic resonance imaging, which is a gentle process per se.
In recent times, increased efforts to solve this problem have been made. For example, new cardiac pacemaker systems have been developed, which are equipped with pacemaker electrode having a specific geometric configuration so as to counteract heating by the alternating electromagnetic fields. The disadvantage here is that these solutions are associated with additional complexity for the implants and may also impair the implant properties. In addition, patients who already have an implant still cannot be examined by magnetic resonance imaging.